1. Field of the Invention
The present invention relates to an ignition timing control apparatus for an internal combustion engine (hereinafter also referred to as an engine) having a plurality of cylinders, and more particularly, to novel technical improvements for suppressing the occurrence of knocking (hereinafter referred to also as a “knock”) thereby to obtain high power.
2. Description of the Related Art
Conventionally, in an ignition timing control apparatus for an internal combustion engine, the ignition timing is retarded (controlled to a retard angle side) or advanced (controlled to an advance angle side) in accordance with the presence or absence of the occurrence of a knock (see, for example, a first patent document: Japanese patent application laid-open No. S58-53675). Also, there has been proposed that when a knock occurs in either of a plurality of cylinders, the ignition timing of all the cylinders is uniformly controlled to a retard angle side (see, for example, a second patent document: Japanese patent application laid-open No. S58-165574). In addition, there has been proposed that the occurrence of a knock is detected for each cylinder, and the ignition timing of a knocking cylinder (i.e., a cylinder in which a knock occurs) is independently retarded (see, for example, a third patent document: Japanese patent application laid-open No. S59-25081).
Further, there has been proposed an ignition timing control apparatus for an internal combustion engine which calculates the ignition timings of individual cylinders from a plurality of ignition timing maps set in advance for the individual cylinders, in order to avoid excessive retard angle control when all the cylinders are uniformly controlled to a retard angle side upon occurrence of a knock in a cylinder (see, for example, Japanese patent application laid-open No. H9-242655). Furthermore, there has also been proposed an ignition timing control apparatus for an internal combustion engine which, in order to avoid the excessively continuous occurrences of knocks when the ignition timings are controlled independently for individual cylinders, in case where knocking occurs in succession in the same cylinder, the ignition timing of the knocking cylinder alone is set to a retard angle side, whereas in case where knocking occurs in succession not in one and the same cylinder but in a plurality of cylinders, the ignition timings of all the cylinders are set to a retard angle side (see, for example, a fifth patent document: Japanese patent application laid-open No. S62-195465).
In the conventional ignition timing control apparatuses for an internal combustion engine, the ignition timings of all the cylinders are controlled to be uniformly retarded upon the occurrence of a knock, as in the above-mentioned second patent document, the ignition timings of all the cylinders are controlled to be uniformly retarded in accordance with the knock that occurred in a cylinder of which the knocking limit ignition timing is the latest among those of the plurality of cylinders in spite of the fact that the ignition timing at which a knock occurs (hereinafter referred to as a “knocking limit ignition timing”) is different from one cylinder to another. As a result, there arises a problem that those cylinders whose knocking limit ignition timings are at a relatively advance angle side are operated in excessively retard ignition angle states, thus giving rise to output power loss.
In addition, in case where all the cylinders are uniformly controlled to a retard angle side, as stated above, the occurrence of knocking concentrates on a cylinder of which the knocking limit ignition timing is in a relatively retard angle side, among the plurality of cylinders, so there is the following problem. That is, the cylinder on which the occurrence of knocking concentrates and its related cylinder block is more greatly deteriorated in comparison with the other cylinders of which the knocking limit ignition timings are in a relatively advance angle side, thus leading to the possibility that the engine might be finally damaged.
Moreover, in case where the ignition timings for the individual cylinders are controlled independently of one another, as in the above-mentioned third patent document, the amount of retard angle corresponding to the occurrence of a knock is first reflected in actuality in the next ignition cycle of the knocking cylinder, so the amount of retard angle corresponding to the occurrence of a knock is not reflected on the other cylinders in spite of the fact that there is a possibility of the occurrence of knocking. As a result, there will arise a problem that knocking continuously occurs in an excessive period of time, thus giving rise to the possibility of deteriorating the audibility or auditory sensation of the user.
Further, in case where the ignition timing of each cylinder is calculated from a map for the purpose of avoiding output torque loss during uniform retard angle control, as in the above-mentioned fourth patent document, no consideration is given to the variation of the knocking limit ignition timing resulting from the individual variation of the engine or the variation of the knocking limit ignition timing due to aging. Thus, there is also the following problem. That is, the ignition timing can not always be set to optimum ignition timing in each of the cylinders, and hence it is after all impossible to avoid the loss of output torque to a satisfactory extent.
On the other hand, as disclosed in the above-mentioned fourth patent document, in case where, when continuous knocking occurs in the same cylinder, the ignition timing of the knocking cylinder alone is controlled to a retard angle side for the purpose of avoiding the occurrence of continuous knocking during independent retard ignition angle control, whereas when continuous knocking occurs in other than the one and same cylinder, the ignition timings of all the cylinders are uniformly controlled to a retard angle side, all the cylinders are controlled to be retarded in accordance with the result of the determination of the occurrence of continuous knocking based on the frequency of knock occurrences. Accordingly, two to several knocks will continuously or successively occur, so the audibility or auditory sensation of the user will be deteriorated even with the occurrence of a minimum of two excessively large continuous knocks, thus resulting in a problem of reduced marketability in comparison with the case where uniform retard ignition angle control is carried out.